Hi all! What a great forum. I have an 89 GTA in Fire Red, 5.7 L98 automatic and factory T-tops that I acquired as a project.

The wiring for the cooling fans has been butchered so they never come on and it overheats. I'm looking for some help in figuring out how to diagnose this issue.

The temp gauge in the car works fine. I am assuming there is only one coolant temp sender, and that is to the gauge?
There is a cheap aftermarket relay screwed to the radiator support that is connected to the harness near the battery.
There is a splice in that wiring harness near the battery positive terminal. On a hunch, I jumpered to it from the positive battery terminal, and the right hand fan runs.

On the lift, there is an electrical plug, connected to a fitting on the bottom of the left hand fan housing. There is an identical plug dangling there not connected to anything. I'm really confused by the whole thing.

Questions:
Where is the trigger signal for the fans to come on generated? Is it the ECM once the temp output of the coolant temp sender hits a certain voltage?
I am pretty certain there would be a factory relay triggered to pass on the higher current to the fan motors. Where is it?
What is the best way to determine what is failed in this system?

Thanks for any help!!!


EDIT: the Forum algorithm suggested several really informative threads, I copypasta all of them so I can use the information to trace and repair the wiring as well as DX any failed components. What an awesome feature!

 

IIRC the ecm turns on fan 1 . the fan switch in the passenger head between 6 and 8 turns on the 2nd one. the switch is easy to see from under the car. The plug is notorious for becoming brittle and crumbling from heat. One way to test is to unplug and ground the plug. the fans should turn on.

 

This is excellent data, however note turning on the ac will activate the fans as well.

I pillage the dual speed dual fan harness & relays out of late 90s Cadillac D’Elegance when I find them. Much quieter, better cooling & less demanding on the electrical.